Gerald R Popelka, PhD

Consulting Professor of Otolaryngology

Otolaryngology (Head and Neck Surgery)

Bio

Bio

Gerald R Popelka holds a PhD degree from the University of Wisconsin with an emphasis in neuroscience, and a two year post doctoral research fellowship in otolaryngology from UCLA. Prior to these he earned a masters degree in audiology from Kent State University. He was a faculty member for 24 years at Washington University in St. Louis and joined the faculty at Stanford in 2004.

Dr. Popelka?s research has been funded continuously with grants from a wide variety of agencies. He has initiated and completed successful collaborative research projects among diverse academic divisions including otolaryngology, neurology, neurosurgery and engineering.

Dr. Popelka is a co-inventor of the world?s first all digital hearing aid. The resulting patent forms the basis of every digital hearing aid, virtually all hearing aids currently produced worldwide. In 1996 he conceived and lead the development of JARO, the peer-reviewed Journal of the Association for Research in Otolaryngology, now recognized as a premier, high impact international auditory scientific research journal that was launched in 2000.

With over 125 research articles, many research presentations, two college textbooks, and various achievement awards, he has developed an international reputation for creating and using leading-edge technology that addresses both basic science and clinical applications. He remains in the forefront of developing innovative technology for biomedical applications currently focusing on basic auditory neuroscience and effective teletherapy models for hearing-impaired children.

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Research & Scholarship

Current Research and Scholarly Interests

Primary tinnitus is defined as an auditory percept in the absence of a sound source that affects ~15% of the population with 2% severely impaired. Though many theories have been proposed concerning etiology, the neuronal fingerprint of primary tinnitus is the altered spectral power of electroencephalography/magnetoencephalography (EEG/MEG) signals over a large network of brain areas.

Current understanding of tinnitus is very limited. A number of therapeutic options have been proposed including cognitive behavioural therapy, hearing aids, cochlear implants, sound maskers, retraining therapy, medication, vitamins, dietary supplements, hyperbaric oxygen, acupuncture and neuromodulation therapy. Currently there is no standard of care. Published studies demonstrate little consensus with large variability in outcomes.

Neuromodulation therapy is the only approach intended to directly affect neural circuits in the brain to produce long lasting effects after intervention. A variety of neuromodulation therapy signals have been investigated including electromagnetic, electrical, ultrasound and acoustic. Neuromodulation therapy can be invasive if the signals are delivered directly to the brain during surgery or via implanted stimulators, or non-invasive if delivered transcranially or via a sensory system. Most neuromodulation intervention uses signals not specific to the auditory system and can influence adjacent neuronal circuits.

Acoustic coordinated reset neuromodulation therapy is a form of non-invasive neuromodulation therapy specifically for treating primary tonal tinnitus. It uses acoustic signals delivered directly to the ear and therefore limits the exposure to only the auditory neural tracts. The acoustic signals are tailored to the characteristics of the tinnitus percept itself, additionally limiting the intervention to the actual source of the tinnitus. The approach is based on well accepted theoretical neuroplasticity principles and developed with computational modelling. The therapy uses sequences of acoustic stimuli that target areas of pathological neural synchrony within the brain and intended to induce a sustained reduction of the strength of synaptic connectivity among neurons within the affected cell population after therapy completion. Utilizing the highly systematic anatomical tonotopic organization of the peripheral and central auditory system, in particular the auditory cortex, acoustic tones centered on the frequency of the patient?s tinnitus percept are determined and delivered in non-simultaneous sequences several hours per day for several weeks.

Preliminary evidence of the efficacy of acoustic neuromodulation therapy is very promising including statistically and clinically significant reductions in tinnitus loudness and annoyance and improvements in tinnitus questionnaire results. In addition, pre-treatment abnormal EEG power spectra in the ?, ? and ? bands return to more normal values after treatment.

Current research efforts are centered on optimizing tinnitus measures, determining the most effective stimulus frequencies, levels and sequences and insuring accurate and reliable methods of signal delivery. Experiments involve automated tinnitus loudness and pitch matching to create the therapy signals, high density 3D EEG measures (256 electrodes) for localizing tinnitus sources within the brain and tinnitus measures after therapy.

Projects

BabyTalk, Stanford (8/1/2012 - Present)

A teletherapy program for hearing impaired children

Location

Northern California

Listen to Me!, Stanford (8/1/2008 - Present)

Summer institute, Extension and Scholars program for hearing impaired children.

Abstract

Five databases were mined to examine distributions of air-bone gaps obtained by automated and manual audiometry. Differences in distribution characteristics were examined for evidence of influences unrelated to the audibility of test signals.The databases provided air- and bone-conduction thresholds that permitted examination of air-bone gap distributions that were free of ceiling and floor effects. Cases with conductive hearing loss were eliminated based on air-bone gaps, tympanometry, and otoscopy, when available. The analysis is based on 2,378,921 threshold determinations from 721,831 subjects from five databases.Automated audiometry produced air-bone gaps that were normally distributed suggesting that air- and bone-conduction thresholds are normally distributed. Manual audiometry produced air-bone gaps that were not normally distributed and show evidence of biasing effects of assumptions of expected results. In one database, the form of the distributions showed evidence of inclusion of conductive hearing losses.Thresholds obtained by manual audiometry show tester bias effects from assumptions of the patient's hearing loss characteristics. Tester bias artificially reduces the variance of bone-conduction thresholds and the resulting air-bone gaps. Because the automated method is free of bias from assumptions of expected results, these distributions are hypothesized to reflect the true variability of air- and bone-conduction thresholds and the resulting air-bone gaps.

Abstract

Sensorineural hearing loss from sound overexposure has a considerable prevalence. Identification of sound hazards is crucial, as prevention, due to a lack of definitive therapies, is the sole alternative to hearing aids. One subjectively loud, yet little studied, potential sound hazard is movie theaters. This study uses smart phones to evaluate their applicability as a widely available, validated sound pressure level (SPL) meter. Therefore, this study measures sound levels in movie theaters to determine whether sound levels exceed safe occupational noise exposure limits and whether sound levels in movie theaters differ as a function of movie, movie theater, presentation time, and seat location within the theater.Six smart phones with an SPL meter software application were calibrated with a precision SPL meter and validated as an SPL meter. Additionally, three different smart phone generations were measured in comparison to an integrating SPL meter. Two different movies, an action movie and a children's movie, were measured six times each in 10 different venues (n = 117). To maximize representativeness, movies were selected focusing on large release productions with probable high attendance. Movie theaters were selected in the San Francisco, CA, area based on whether they screened both chosen movies and to represent the largest variety of theater proprietors. Measurements were analyzed in regard to differences between theaters, location within the theater, movie, as well as presentation time and day as indirect indicator of film attendance.The smart phone measurements demonstrated high accuracy and reliability. Overall, sound levels in movie theaters do not exceed safe exposure limits by occupational standards. Sound levels vary significantly across theaters and demonstrated statistically significant higher sound levels and exposures in the action movie compared to the children's movie. Sound levels decrease with distance from the screen. However, no influence on time of day or day of the week as indirect indicator of film attendance could be found.Calibrated smart phones with an appropriate software application as used in this study can be utilized as a validated SPL meter. Because of the wide availability, smart phones in combination with the software application can provide high quantity recreational sound exposure measurements, which can facilitate the identification of potential noise hazards. Sound levels in movie theaters decrease with distance to the screen, but do not exceed safe occupational noise exposure limits. Additionally, there are significant differences in sound levels across movie theaters and movies, but not in presentation time.

Abstract

Objective: To compare the effectiveness of two types of treatment for unilateral hearing loss (UHL), bone-anchored hearing instruments (BAHI) and a dental device (SoundBite). Design: Either BAHI or SoundBite were worn for 30 days, and then the devices were swapped and the second device was worn for 30 days. Measures included unaided and aided sound-field thresholds, sound localization, and perception of speech in babble. The APHAB questionnaire was administered for each trial period. Study sample: Nine adult BAHI wearers with UHL. Results: Mid-frequency aided thresholds were lower for SoundBite than for BAHI. Both devices gave benefits for localization after 30 days, but there was no difference between devices. Speech perception was better for both devices than for unaided listening when the target speech came from the poorer hearing side or in front, and the interfering babble came from the better-hearing side. There was no consistent difference between devices. APHAB scores were better for SoundBite than for BAHI. Conclusions: Speech perception and sound localization were similar for the two types of device, but the SoundBite led to lower aided thresholds and better APHAB scores than the BAHI.

Abstract

The lack of an adequate standardized method for reporting level of hearing function in clinical trials has hampered the ability of investigators to draw comparisons across studies. Variability in data reported and presentation format inhibits meta-analysis and makes it impossible to accumulate the large patient cohorts needed for statistically significant inference. Recognizing its importance to the field and after a widely inclusive discussion, the Hearing Committee of the American Academy of Otolaryngology-Head and Neck Surgery endorsed a new minimal standard for reporting hearing results in clinical trials, consisting of a scattergram relating average pure-tone threshold to word recognition score. Investigators remain free to publish their hearing data in any format they believe is interesting and informative, as long as they include the minimal data set to facilitate interstudy comparability.

Abstract

Many guidelines for reporting hearing results use the threshold at 3 kilohertz (kHz), a frequency not measured routinely. This study assessed the validity of estimating the missing 3-kHz threshold by averaging the measured thresholds at 2 and 4 kHz. The estimated threshold was compared to the measured threshold at 3 kHz individually and when used in the pure-tone average (PTA) of 0.5, 1, 2, and 3 kHz in audiometric data from 2170 patients. The difference between the estimated and measured thresholds for 3 kHz was within ± 5 dB in 72% of audiograms, ± 10 dB in 91%, and within ± 20 dB in 99% (correlation coefficient r = 0.965). The difference between the PTA threshold using the estimated threshold compared with using the measured threshold at 3 kHz was within ± 5 dB in 99% of audiograms (r = 0.997). The estimated threshold accurately approximates the measured threshold at 3 kHz, especially when incorporated into the PTA.

Abstract

While continuous positive airway pressure (CPAP) is commonly used for obstructive sleep apnea treatment, its effect on middle ear pressure is unknown. The purpose of this study was to measure the effect of CPAP on middle ear pressure and describe the correlation between CPAP levels and middle ear pressures.Retrospective review of normal tympanometry values and a prospective cohort evaluation of subjects' tympanometric values while using CPAP at distinct pressure levels.A total of 3,066 tympanograms were evaluated to determine the normal range of middle ear pressures. Ten subjects with no known history of eustachian tube dysfunction or obstructive sleep apnea had standard tympanometry measurements while wearing a CPAP device. Measurements were taken at baseline and with CPAP air pressures of 0, 5, 10, and 15 cm H(2)O.The percentage of normal control patients with middle ear pressures above 40 daPa was 0.03%. In the study population, prior to a swallowing maneuver to open the eustachian tube, average middle ear pressures were 21.67 daPa, 22.63 daPa, 20.42, daPa, and 21.58 daPa with CPAP pressures of 0, 5, 10, and 15 cm H(2) 0, respectively. After swallowing, average middle ear air pressures were 18.83 daPa, 46.75 daPa, 82.17 daPa, and 129.17 daPa with CPAP pressures of 0, 5, 10, and 15 cm H(2)0, respectively. The postswallow Pearson correlation coefficient correlating CPAP and middle ear pressures was 0.783 (P < 0.001).Middle ear air pressure is directly proportional to CPAP air pressure in subjects with normal eustachian tube function. Middle ear pressure reaches supraphysiologic levels at even minimal CPAP levels. Although further investigation is necessary, there may be otologic implications for patients who are chronically CPAP dependent. These findings may also influence the perioperative practice of otologic and skull base surgeons.

Abstract

To determine the long-term safety and benefit of a new intraoral bone conduction device (SoundBite Hearing System by Sonitus Medical) for single-sided deafness (SSD).A multi-center, controlled, nonrandomized, prospective unblinded study of SSD patients wearing the device over a 6-month period.Ambulatory care centers typical of those where SSD patients are diagnosed and treated.Adults (N = 22) with acquired, permanent SSD and no current use of any other SSD device.Continual daily wear of the new device for 6 months.Comprehensive medical, audiologic, and dental measures; aided thresholds; Abbreviated Profile of Hearing Aid Benefit scores, and an SSD questionnaire.There were no related adverse events or changes in the medical or audiologic findings at the end of the trial compared with the beginning. There were no significant changes in the mean aided thresholds (p > 0.01) or the mean dental measures (p > 0.05) at 3 or 6 months compared with pretrial measures. The mean Abbreviated Profile of Hearing Aid Benefit benefit scores showed improvement (p < 0.01) for the Background Noise, Reverberation, and Ease of Communication subscales and the Global scale at 3 and 6 months. The results of the SSD questionnaire indicated that the vast majority (>90%) of the subjects reported satisfaction and improvement in a variety of areas after wearing the device long term.The SoundBite system is safe and continues to provide substantial benefit for SSD patients with continual daily use over a 6-month period.

Abstract

Classical and subtypes of kernicterus associated with bilirubin toxicity can be differentiated in part with physiological auditory measures that include auditory-evoked potentials and measures of cochlear integrity. The combination of these auditory measures suggests that bilirubin exposure results in auditory system damage initially at the level of the brainstem, progressing to the level of the VIII cranial nerve and then to greater neural centers. There is no evidence of neural damage at the level of the cochlea. Auditory neural damage from bilirubin toxicity ranges from neural timing deficits, including neural firing delays and dyssynchrony, to neural response reduction and even elimination of auditory neural responses. This condition is comprehensively described as auditory neuropathy spectrum disorder. Independent measures of cochlear function and auditory neural function up to the level of the brainstem can effectively diagnose auditory neural damage resulting from bilirubin neurotoxicity. Intervention, including cochlear implants can be effective.

Abstract

To determine the efficacy, benefit, and safety of a new in-the-mouth bone conduction device (SoundBite Hearing System) for single-sided deafness (SSD).A multicenter, controlled, nonrandomized prospective unblinded study of SSD patients wearing the device.Ambulatory care centers typical of those where SSD patients are diagnosed and treated.Adults (ages >18 and <80 yr) with acquired, permanent SSD (N=28) and no current use of any SSD device.Continual daily wear of the new device over a 30-day trial period.The Hearing in Noise Test (HINT), the Abbreviated Profile of Hearing Aid Benefit (APHAB), comprehensive pretrial and posttrial medical, audiologic, and dental examinations and an SSD questionnaire.The Hearing in Noise Test scores improved an average of -2.5 dB after 30 days, compared with wearing no device (p<0.001). The Abbreviated Profile of Hearing Aid Benefit scores improved (p<0.05) for all subjects for the Global and Background Noise subscales and for all but 1 subject for the Reverberation and Ease of Communication subscales. There were no medical, audiologic, or dental complications.The SoundBite system is safe and effective and provides substantial benefit for SSD patients with continual daily use over a 30-day period.

Abstract

Auditory thresholds with standardized clinical procedures are obtained over a much narrower frequency range by bone conduction than by air conduction. As a result, diagnostic information for both sensorineural and conductive-mechanism function is incomplete for high frequencies. A new magnetostrictive bone-conduction transducer that has the potential for improved output in the high-frequency range was evaluated in the laboratory and in a variety of subjects with normal hearing (N=11) or sensorineural hearing loss (N=9). Laboratory results indicated that harmonic distortion and acoustic radiation were both sufficiently low to allow accurate threshold measurements. Auditory thresholds obtained with this magnetostrictive bone-conduction transducer can be measured accurately under conventional clinical conditions for frequencies up to 16 kHz and levels up to 85 dB HL. These measures can be used to accurately characterize sensorineural hearing sensitivity for high frequencies and, when combined with standard air-conduction measures for high frequencies, to accurately characterize conductive-mechanism function for frequencies higher than possible with current diagnostic bone-conduction technology.

Abstract

A real-time MRI "movie" during natural sleep ("Sleep MRI") allows observation of dynamic airway obstructions in obstructive sleep apnea syndrome (OSAS) patients. The purpose of this article was to determine the reliability of assessing these obstructions.Cross-sectional diagnostic test evaluation.Academic referral center.A total of 23 Sleep MRI sequences randomly selected from 20 consecutive OSAS patients were analyzed by two experienced sleep surgeons on two separate occasions separated by at least two weeks. Five dimensions were assessed: presence or absence of any obstruction, presence or absence of a retropalatal obstruction, presence or absence of a retroglossal obstruction, presence or absence of a swallow, and duration of an obstructive event.For all dimensions measured, intra-rater reliability coefficients ranged from a low of 0.95 to a high of 1.0 for each rater. Inter-rater reliability coefficients ranged from a low of 0.85 to a high of 1.0. On two separate evaluations separated by at least two weeks, rater 1 identified a retropalatal obstruction in 100 percent of sequences, whereas rater 2 did so in 91 percent and 96 percent of the sequences, respectively. Retroglossal obstruction was identified in 57 percent (rater 1) and 65 percent (rater 2) of sequences.Intra-rater and inter-rater reliability coefficients are very high for determination of presence or absence of any obstruction, presence or absence of a retropalatal obstruction, presence or absence of a retroglossal obstruction, presence or absence of a swallow, and duration of obstruction from Sleep MRI sequences in OSAS patients.

Abstract

A new intraoral bone-conduction device has advantages over existing bone-conduction devices for reducing the auditory deficits associated with single-sided deafness (SSD).Existing bone-conduction devices effectively mitigate auditory deficits from single-sided deafness but have suboptimal microphone locations, limited frequency range, and/or require invasive surgery. A new device has been designed to improve microphone placement (in the ear canal of the deaf ear), provide a wider frequency range, and eliminate surgery by delivering bone-conduction signals to the teeth via a removable oral appliance.Forces applied by the oral appliance were compared with forces typically experienced by the teeth from normal functions such as mastication or from other appliances. Tooth surface changes were measured on extracted teeth, and transducer temperature was measured under typical use conditions. Dynamic operating range, including gain, bandwidth, and maximum output limits, were determined from uncomfortable loudness levels and vibrotactile thresholds, and speech recognition scores were measured using normal-hearing subjects. Auditory performance in noise (Hearing in Noise Test) was measured in a limited sample of SSD subjects. Overall comfort, ease of insertion, and removal and visibility of the oral appliance in comparison with traditional hearing aids were measured using a rating scale.The oral appliance produces forces that are far below those experienced by the teeth from normal functions or conventional dental appliances. The bone-conduction signal level can be adjusted to prevent tactile perception yet provide sufficient gain and output at frequencies from 250 to 12,000 Hz. The device does not damage tooth surfaces nor produce heat, can be inserted and removed easily, and is as comfortable to wear as traditional hearing aids. The new microphone location has advantages for reducing the auditory deficits caused by SSD, including the potential to provide spatial cues introduced by reflections from the pinna, compared with microphone locations for existing devices.A new approach for SSD has been proposed that optimizes microphone location and delivers sound by bone conduction through a removable oral appliance. Measures in the laboratory using normal-hearing subjects indicate that the device provides useful gain and output for SSD patients, is comfortable, does not seem to have detrimental effects on oral function or oral health, and has several advantages over existing devices. Specifically, microphone placement is optimized for reducing the auditory deficit caused by SSD, frequency bandwidth is much greater, and the system does not require surgical placement. Auditory performance in a small sample of SSD subjects indicated a substantial advantage compared with not wearing the device. Future studies will involve performance measures on SSD patients wearing the device for longer periods.

Abstract

A portable, prototype instrument that measures peak CO, CO2 and H2 concentrations of breath samples was evaluated on 58 antibody positive, blood group incompatible infants. The reproducibility of 108 duplicate breath CO determinations improved when the result was normalized (CO(n)) for the simultaneously measured CO2 concentration (r = 0.97 versus r = 0.87). The average CO(n) for 18 antibody positive, ABO incompatible infants who received phototherapy was 1.2 ppm higher than the average for 32 who did not receive phototherapy (p < 0.001). There was a positive correlation between CO(n) and the duration of phototherapy (r = 0.75). Sodium acetate infusion and breath H2 did not affect the CO(n) results. In antibody positive infants, single breath CO to CO2 ratios provided more reproducible results than CO determinations that were not adjusted for the CO2 concentration. Therefore, a portable instrument that measures both gases on the same aliquot of exhaled air and that is not affected by H2 should have clinical utility as an indicator of heme catabolism and bilirubin production that is not distorted by hyper- or hypoventilation.

Abstract

We sought to develop techniques for visualizing cochlear blood flow in live mammalian subjects using fluorescence microendoscopy.Inner ear microcirculation appears to be intimately involved in cochlear function. Blood velocity measurements suggest that intense sounds can alter cochlear blood flow. Disruption of cochlear blood flow may be a significant cause of hearing impairment, including sudden sensorineural hearing loss. However, inability to image cochlear blood flow in a nondestructive manner has limited investigation of the role of inner ear microcirculation in hearing function. Present techniques for imaging cochlear microcirculation using intravital light microscopy involve extensive perturbations to cochlear structure, precluding application in human patients. The few previous endoscopy studies of the cochlea have suffered from optical resolution insufficient for visualizing cochlear microvasculature. Fluorescence microendoscopy is an emerging minimally invasive imaging modality that provides micron-scale resolution in tissues inaccessible to light microscopy. In this article, we describe the use of fluorescence microendoscopy in live guinea pigs to image capillary blood flow and movements of individual red blood cells within the basal turn of the cochlea.We anesthetized eight adult guinea pigs and accessed the inner ear through the mastoid bulla. After intravenous injection of fluorescein dye, we made a limited cochleostomy and introduced a compound doublet gradient refractive index endoscope probe 1 mm in diameter into the inner ear. We then imaged cochlear blood flow within individual vessels in an epifluorescence configuration using one-photon fluorescence microendoscopy.We observed single red blood cells passing through individual capillaries in several cochlear structures, including the round window membrane, spiral ligament, osseous spiral lamina, and basilar membrane. Blood flow velocities within inner ear capillaries varied widely, with observed speeds reaching up to approximately 500 microm/s.Fluorescence microendoscopy permits visualization of cochlear microcirculation with micron-scale optical resolution and determination of blood flow velocities through analysis of video sequences.

Abstract

Accurate assessment of neonatal hearing screening performance is impossible without knowledge of the true status of hearing, a prohibitive requirement that necessitates a complete diagnostic evaluation on all babies screened. The purpose of this study was to circumvent this limitation by integrating two types of screening measures obtained near simultaneously on every baby. Peripheral auditory function was defined by otoacoustic emission results. A complete diagnostic evaluation was performed on every baby who received a "Refer" outcome for auditory brainstem response screening. The integrated results for auditory brainstem response screening in an unselected group of 300 newborns estimated sensitivity at 100%, specificity at 99.7%, overall referral rate at 2.0%, and a positive predictive value of 83.3%. Conductive loss associated with amniotic fluid in the middle ear can persist several weeks after birth; conductive loss can produce a "Refer" outcome for auditory brainstem response screening; and auditory neuropathy can be detected with screening measures. Prevalence results were consistent with the published literature. The implications of this study are that otoacoustic emissions and auditory brainstem measures provide much more information than either alone and that both are needed for a comprehensive hearing screening program.

Abstract

The objective of this study was to identify individual sources of noise and their contribution to the overall noise that influences valid measurement of otoacoustic emissions in neonates. The hypothesis was that careful selection of eliciting signals and signal processing parameters, unique analysis of measured results, and control of certain subject characteristics would allow isolation of these individual noise sources and determine their relative influence.Eliciting signal parameters were optimized and held constant to minimize equipment noise. Analysis of noise floors in relation to signal level was used to identify equipment-related noise associated with changes in signal parameters. Analysis of noise floor distributions was used to determine whether environmental noise entered the measurements via inadequate coupling of the probe to the ear. The acoustic characteristics of the middle ear were varied via subject selection to determine the influence of middle-ear characteristics on noise floor levels.The two sources of noise associated with the measurement equipment need not contribute to the noise floor for biologically relevant otoacoustic emissions measurements (eliciting signal levels between 30 and 75 dB SPL). Of the two pathways identified for environmental noise, the pathway resulting from an inadequate seal between the probe and the ear canal can be eliminated. One of the two sources of noise related to the subject, noise resulting from biologic activity unrelated to the ear can be minimized. However, the remaining factor, the status of the middle ear, has been shown to contribute as much as 6 dB to the overall noise floor.Careful selection of signal parameters and additional data analyses and procedural variables can isolate or control several sources of noise that influence distortion product otoacoustic emission measurements in neonates. Tight coupling between the probe unit and the external ear canal should be maintained for all measurements. Middle ear abnormalities can increase noise floors up to 6 dB.

Abstract

Distortion product otoacoustic emissions (DPOAEs) for low stimulus levels (< 60 dB SPL) have been reported in adult humans under ideal conditions. In neonates, DPOAEs have been reported only for high-level stimuli. The purpose of this paper was to determine characteristics of the 2f1-f2 DPOAE for low-level stimuli in neonates and to assess the feasibility of obtaining such measures in a noisy environment. Subjects were 19 premature neonates presumed to have normal hearing based on systematic pneumatic otoscopy measures and evoked auditory brainstem responses. For stimuli centered at 2000 and 6000 Hz and presented over a range of 30 to 75 dB SPL, DPOAEs were measured employing linear time averaging for up to 128 time frames at each level. In quiescent subjects, the level of the noise floor was as low as that reported in cooperative adults under ideal conditions (approximately -30 dB SPL), and the functions were identical. That is, valid measures were obtained for very low stimulus levels (30 dB SPL), the rate of growth approached 1 dB/dB, and identical nonmonotonicities (saturation, plateaus, and notches) were observed as those reported for adults. When the noise floor was elevated due to subject activity, no valid data could be obtained for low-level stimuli even though the DPOAEs were at expected levels for high-level stimuli. These results have important implications for the use of such measures in this population because the DPOAEs associated with the metabolically active nonlinear cochlear processes at low stimulus levels may be contaminated with DPOAEs associated with other processes at high stimulus levels.

Abstract

This study addressed the hypotheses that the growth of the level of distortion product otoacoustic emissions (LDP) with primary-tone level reflects the behavior of a third-order nonlinear polynomial system, and that two sources exist for these distortion products. The results indicated that the 2f1-f2 otoacoustic emission in humans can be measured over a much larger stimulus range than reported previously, even for stimuli (L1 = L2) as low as 10 dB SPL (re 20 microPa). The input/output functions are best described as a straight line with a rate of growth of about 1 dB/dB of stimulus level. For stimulus levels at which metabolically active, nonlinear cochlear processes are in operation, the system does not behave as a simple third-order nonlinear polynomial. Small plateaus and sharp discontinuities or 'notches' can occur in the functions at stimulus levels of approximately 55 dB SPL. These characteristics are consistent with the notion of two separate sources of the LDP, one at low stimulus levels, and one at high levels. An alternative explanation is that the measured otoacoustic emission does not represent only the activity at a single location along the basilar membrane but includes the effects of interactions among similar signals arising from multiple locations, or from the original source via multiple paths.

Abstract

Parametric variations in the ratio of primary-tone frequencies were explored to optimize the amplitude of the 2f1-f2 distortion product otoacoustic emission for clinical purposes. Ten ears from 5 normally hearing human subjects were examined with primary tones geometrically centred around the standard audiometric frequencies of 0.5, 1, 1.5, 2, 3, 4, 6 and 8 kHz. The distortion product at the frequency 2f1-f2 (f1 < f2) was measured at six probe tone frequency ratios (f2:f1) varying between 1.15 and 1.40 using equal level primaries of 75 dB SPL. The results showed that a single f2:f1 ratio between 1.20 and 1.25 provides a reasonable value for clinical use in that it optimizes the magnitude of the distortion product at 2f1-f2, provides for sufficient resolution in the test frequency range, and is applicable to the standard clinical test frequencies.

Abstract

The effect of systematic variations in the relative levels (L1, L2) of two primary tones (f1, f2) on the amplitude of the distortion product otoacoustic emission (DPOAE) at 2f1-f2 and f1 < f2 was investigated in 14 ears from 7 normally hearing human subjects. The primary tones (f2:f1 = 1.23) were geometrically centred at the standard clinical frequencies of 0.5, 1, 1.5, 2, 3, 4, 6 and 8 kHz. The quantity L1-L2 was varied systematically from -10 dB through + 10 dB with L2 held constant at 75 dB SPL for negative values, L1 held constant at 75 dB SPL for positive values, and L1 = L2 = 75 dB SPL at 0 dB relative difference. The maximum amplitudes of the distortion products were generated when L1 = L2 at all geometric centre frequencies except 8 kHz. The reduction of the DPOAE with reduction of L1 was linear at a rate that gradually increased as a function of geometric mean frequency. To a lesser extent, the reduction of the DPOAE with reduction of L2 also was linear but at a rate that systematically decreased as a function of geometric mean frequency. The results suggest, that to maximize the level of the distortion product for clinical purposes, the relative levels of the primary tones should be equal to each other, at least when overall stimulus levels are around 75 dB SPL and f2:f1 = 1.23.

Abstract

The combined term, sensorineural, is useful because clinical distinction between sensory and neural lesions is often difficult, and because sensory lesions may lead to secondary neural degeneration or, though rarely, a neural lesion may lead to secondary sensory degeneration. The threat of lawsuits for failure to identify treatable neurologic conditions has led to overuse of tests, while fiscal constraints exert pressure to limit expensive diagnostic testing. The purpose of this review of the relation between sensory and neural hearing loss is to provide a practical method to screen for neural lesions using pure-tone thresholds and a single speech discrimination score. The difference between the articulation index and the word recognition score of a patient provides a statistically reliable index of suspicion that may reduce the diagnostic dilemma of neural presbycusis.

Abstract

Although many patients with hearing loss benefit from medical or surgical intervention, the vast majority have noncorrectable hearing disorders for which rehabilitation through amplification is indicated. There are three goals for the application of hearing aids: (1) to amplify normal conversational speech to levels that are maximally understandable to the patient; (2) to help the patient hear other environmental sounds; and (3) to assist in the educational or habilitative process for those children who sustain hearing loss prior to language and speech development. In addition, there are certain issues that require medical consideration when a wearable device is placed in the ear. This article describes current hearing aid technology; reviews its benefits, limitations, and application for typical patients; discusses the medical aspects of hearing aid fitting; and describes new hearing aid technology on the horizon.

Abstract

The hearing sensitivity of 9427 railroad train crew members, determined during the first year of a company-wide hearing conservation program, was compared with hearing sensitivity in a control population not exposed to occupational noise. The hearing sensitivity of the trainmen did not differ significantly from that of the control population. Multiple regression analysis, which considered separately the effects of age and years of service, showed significant differences in hearing levels due to age, but no differences in hearing levels due to years of service. Evaluation of the data by risk categories developed by the National Institute for Occupational Safety and Health indicate that this group of trainmen had no risk of occupational noise-induced hearing loss. These analyses, combined with studies of locomotive cab noise, show clearly that trainmen are not typically exposed to hazardous occupational noise.

Abstract

Speech audibility may be defined as that proportion of a speech spectrum which is above a person's threshold. To optimize speech audibility with a hearing aid, several measures are needed. These include quantification of a speech spectrum, measures of hearing sensitivity, and measures of the "real ear" gain of the hearing aid. Some procedural factors must be considered to obtain adequate measures in a typical clinical setting. Those considered here are: (1) a modified Articulation Index to quantify a speech spectrum, (2) specification of hearing sensitivity with a narrowband sound field reference where the out-of-band rejection rate of the sound field stimulus is greater than twice the slope of the hearing loss, and (3) use of functional gain (measured directly or estimated using earphone and sound field results provided that the sound field stimulus has the required characteristics for measuring hearing sensitivity in the sound field) as a measure of the real ear gain of the hearing aid. Guidelines are given for the practical measurement of speech audibility in a typical clinical setting. The guidelines are appropriate for all measures of real ear gain including those obtained with all probe tube systems.

Abstract

Recent progress on the development of an ear-level digital hearing aid is described. The work includes development of a body-wearable digital hearing aid and a computer-based hearing evaluation system that exploits the flexibility afforded by digital signal processing. The prescriptive criteria and fitting procedure used with the digital hearing aid are described briefly. Design considerations in the development of VLSI chips for an ear-level unit are discussed.

Abstract

Audiometric tests were conducted on 19 subjects with hypophosphatemic bone disease to investigate whether auditory impairment like that reported in affected adults occurs in young patients. No hearing loss or significant auditory findings were noted among the children or young adult patients. However, sensorineural hearing loss of cochlear origin was identified in the three oldest subjects (40 to 58 years), although a history of noise exposure in two of them could explain the observations. The results indicate that if an association exists between hypophosphatemic bone disease and hearing impairment, the auditory signs will not develop until adulthood in treated patients. Additional studies of large populations of affected adults are needed to identify the incidence and mechanism(s) of the auditory system abnormalities and to assess any effect of medical therapy for the metabolic bone disease.

Abstract

Measurements of functional gain were compared first to coupler gain for 57 subjects using one of three hearing aid-earmold combinations and second to probe-tube gain for 12 subjects using in-the-ear hearing aids. The average difference between functional and coupler gain plotted as a function of frequency yielded results that were similar to previous reports, with the greatest effects occurring at 3000 and 4000 Hz. Significant differences were seen among hearing aid-earmold combinations at 3000, 4000, and 6000 Hz. Standard deviations for measurements between 750 and 2000 Hz were less than 5 dB and could be explained by variability of functional gain measures associated with test-retest variability of thresholds measured in a sound field. Below 750 Hz and above 2000 Hz, standard deviations exceeded 5 dB. The greater variability may be explained by differences in earmold venting, acoustic characteristics of the ear canal, and stimuli used to measure functional and coupler gain. Neither room nor hearing-aid noise appeared to affect the results significantly. When functional gain was compared to insertion gain measured with a probe-tube system, the average difference across frequencies was less than 1 dB. The variability of the differences at all frequencies, with the exception of 6000 Hz, was within the range reported for functional gain measurements. It was concluded that functional gain can be accurately estimated using probe-tube measurements.

Abstract

Auditory evoked potentials are nearly all on-effects and the 'effective stimuli' for them are necessarily brief. Their frequency specificity is therefore limited, especially for the brainstem responses, because of the well-known trade-off between duration and frequency specificity. Brainstem responses are of special interest because they are unchanged in the sleep-like sedation that is required for difficult-to-test children. The middle-latency responses do not meet this requirement. Two patterns of tone burst that are appropriate and promising for the slow cortical potentials and for brainstem potentials, respectively, have rise and fall times of 2 periods of the modulated tone and plateaus of 10 (or 7) periods and 1 period, respectively. Their behavioral thresholds are nearly insensitive to difference in repetition rate between 4 and 40 stimuli/s. Their peak equivalent SPL threshold values at 500, 1 000, 2 000 and 4 000 Hz have been determined for 16 otologically normal ears. Using these reference levels, audiograms have been obtained for subjects with impaired hearing. The audiograms for 'flat' hearing losses do not differ significantly from the corresponding conventional pure-tone audiograms. The slopes for steep high-frequency hearing losses are underestimated, however, particularly with the brief (2-1-2) pattern. Nevertheless, the 2-1-2 pattern appears to be close to the best possible compromise.

Abstract

After a varied history over the past 15 years, basic acoustic immittance measures now include certain physical measures and certain physiological measures. This article reviews current concepts in the terminology and the instrumentation used for these basic measures. It is designed to provide an understanding of standard acoustic immittance measures and a framework for interpreting the results of special acoustic immittance procedures discussed in this issue.

Abstract

Audiologic findings in a child who received a single-channel cochlear implant are presented. The measures used were threshold sensitivity to frequency-specific stimuli and results on various subtests from the Test of Auditory Comprehension (Trammel, 1976), the Monosyllable, Trochee, Spondee Test (Erber & Alencewicz, 1976), and the Minimal Auditory Capabilities Battery (Owens, Kessler, Telleen, & Schubert, 1981). The results for the implanted ear indicated uneven change in performance across measures compared to results with conventional amplification prior to receiving the implant. Performance of the implanted ear did not approach performance of the better contralateral ear. Observations by teachers and guardians indicated that there was no apparent change in auditory performance even after the cochlear implant had been worn for 6 months. Overall there was no evidence that the cochlear implant worn for 6 months provided any practical benefit to this child.

Abstract

The specific contribution of admittance procedures in the diagnosis of hearing impairment was studied in a group of 53 handicapped children. The value of admittance procedures was assessed in relation to that of otoscopy and pure tone audiometry. Admittance procedures and otoscopy were successfully performed in all but one of the children and indicated conductive pathology in about 40% of the subjects, whereas pure tone audiometry was not feasible or inconclusive in 30.2% of the subjects. In 5.7% of the subjects admittance procedures proved the only diagnostic tool.

Abstract

Acoustic conductance and susceptance tympanograms were obtained at 220 and 660 Hz in 34 neonates. The neonates were categorized into three age groups (8-24 hours, 24-60 hours, and 60-96 hours). Single-peaked, double-peaked, and monotonically increasing tympanograms were found. Static values for conductance, susceptance, admittance, resistance, reactance and impedance at the lateral surface of the tympanic membrane were computed from the tympanograms. There were no significant differences in mean static values among the three groups. At 220 Hz, the individual static reactance values were usually smaller than the static resistance values and often assumed a positive sign. At 660 Hz, the individual static reactance values always assumed a negative sign and were approximately equal to the static resistance values. The single- and double-peaked tympanograms apparently were the result of previously identified interactions between static resistance and reactance values. The data were compared to those of infants and adults. Tympanograms at 220 Hz were obtained for 13 of the original subjects at the age of three to four months. The data collected in this group were consistent with those reported in the literature for the same age group.

Abstract

The growth function of the acoustic stapedius reflex was measured in subjects with normal hearing and sensorineural hearing loss of cochlear origin. The effects of age and magnitude of hearing loss were controlled. Activating stimuli were 500, 1000, and 2000 Hz tones and broadband noise. Stapedius muscle activity was inferred from acoustic impedance measures in the contralateral ear. The mean growth functions for tones were essentially linear in log-log plots with the rate of growth equal for the two groups. The mean growth function for the noise signal was curvilinear for the normal hearing groud had linear for the hearing loss group. Comparison of slope functions derived from the fitted data indicated that the rate of reflex growth for the noise signal, over a limited range above reflex threshold, is greater in ears with cochlear lesions than normal ears. For higher level noise signals, however, the rate of reflex growth is similar for normal and pathological ears. The effect of a cochlear lesion on the input-output function of the cochlea for both tonal and noise stimuli is to maintain the rate of reflex growth but shift the function along the intensity axis of a tonal signal and the response axis for a noise signal.

Abstract

Tympanometry was performed before and after producing specific lesions in the middle ears of cats. The lesions selected for study included stapes fixation, ossicular discontinuity, and scarred tympanic membranes. Stapes fixation resulted in marked increases in middle ear impedance, easily detected with tympanometry. Ossicular discontinuity resulted in complex tympanometric shapes which were easily accounted for by simple interactions between acoustic resistance and reactance. The complex shapes that occurred in normal and abnormal ears with pressure changing from negative to positive resulted from more complicated interactions. Large surgical incisions in the posterior-superior quadrant of the eardrum were quite visible at otoscopy but could not be detected tympanometrically one month after surgery.

Abstract

Previous studies which have measured acoustic-reflex responses to bone-conducted signals have not effectively differentiated reflex responses from artifacts. A convenient method for identifying such artifacts was developed and employed on some acoustic-reflex measures for bone-conducted signals. The findings indicated that artifacts result when a frequently-used acoustic admittance meter (Grason-Stadler 1720B) and a conventional bone vibrator were used to measure reflex responses for tonal and noise-activating signals. It was suggested that the method be employed in future studies which investigate the acoustic reflex in response to bone-conducted signals.

Abstract

To gain a better understanding of tympanometric results that have been difficult to interpret, such as asymmetrical and W-shaped tympanograms, acoustic susceptance and conductance tympanograms were measured from subjects with normal hearing and from subjects with well-defined middle ear pathology. Acoustic reactance, resistance, and impedance were computed and predicted from the measured data. Asymmetrical tympanograms derive in large part from the marked asymmetry in acoustic resistance as a function of ear canal pressure. W-shaped tympanograms result from interactions between reactance and resistance that occur when the two quantities assume similar absolute values or when reactance is mass controlled. A criterion for distinguishing between W-shaped tympanograms that are normal from those that are abnormal is discussed.

Abstract

Tympanometry and acoustic reflex threshold data are reported for a series of presumable normal infants ranging in age from 55 to 132 days. In general, tympanograms displayed single peaks between +/- 50 mm H2O. Susceptance tympanograms with a 660-Hz probe frequency were sometimes characterized by monotonically increasing susceptance as ear canal pressure was changed from -200 to +200 mm H2O. Static values of acoustic conductance, susceptance, admittance, resistance, reactance, impedance, and phase angle were computed from tympanograms using the values of ambient and +200 mm H2O (0/+200 procedure) and maximum and minimum tympanometric values (MAX/MIN procedure). Comparison of the data from the two computational procedures suggested that the MAX/MIN procedure produces means and standard deviations of static values which are more manageable for establishing confidence limits with which to evaluate potentially pathological subjects. The MAX/MIN procedure resulted in lower mean values of conductance and susceptance for infant subjects relative to previously reported adult data using a similar computational procedure. Acoustic reflex thresholds were clearly present in all testable infants at coupler sound pressure levels similar to adult data, suggesting that the relations between reflex thresholds and hearing sensitivity demonstrated in adult subjects are similarly applicable to infant subjects. Mild sedation to induce sleep without altering the reflex would make acoustic reflex threshold measurement a useful procedure for screening large numbers of infants.